Baseline metrics of traditional
reinforcement materials
Consider the force-elongation curve of the two most commonly used materials for carcass reinforcement: Polyester high modulus low shrinkage (PET HMLS) and Rayon. The force-elongation curves presented for each cord reflect the level of twist required to withstand compression fatigue, which is a critical factor in carcass design.
RAYON
+ High modulus + Good fatigue properties - Low strength
PET HMLS
+ High strength + Good fatigue properties - Low modulus

For heavier EV and SUV tires, the strength of Rayon and the modulus of PET HMLS are insufficient.